1. Field of the Invention
The present invention relates to an ink-jet recording head and a process for making same. In particular, the invention relates to an ink-jet recording head having a body which is a laminate of green sheets made of piezoelectric material. Each of the sheets has films formed in it. At the same time that the sheets are laminated, the films are laminated to form leading electrodes integrally in the head body. The electrodes will be connected to piezoelectric actuators.
2. Description of Related Art
A conventional ink jet printer has ink jet nozzles communicating with ink passages, which can be supplied with ink from an ink supply source. Droplets of ink can be ejected from the nozzles. Printers of such a type have been popular which can be small, which can make high speed recording, and which use on-demand systems, and particularly pressure control systems or bubble control systems by means of heat.
Ink jet printers which use pressure control systems have been made practicable and proposed which use piezoelectric systems with piezoelectric ceramics or other elements.
FIGS. 14-16 of the accompanying drawings show the ink jet head 100 of a conventional ink jet printer using such piezoelectric system. The head 100 includes a body 101, which has ink passages 111 each defined between partition walls 114 made of piezoelectric material. The passages 111 can be supplied with ink from an ink supply source through a manifold. As shown in FIG. 16, an electrode 112 is formed on each side surface of each partition 114. As shown in FIG. 14, a drive IC 107 is formed on a printed board 119. While a drive signal is supplied for a predetermined slight time from the drive IC 107 to the electrodes 112 on the adjoining partitions 114 associated with the passage 111 through which ink should be ejected, these partitions 114 are deformed by shearing strain in such a manner that the passage 111 enlarges in volume to be replenished with ink. When the deformed partitions 114 return to their original shape, ink is ejected from the passage 111 out through the nozzle 110 at the front end of the passage.
The head body 101 also has leading electrodes 105 formed on its top to feed the electrodes 112 of the actuators each formed for one of the passages 111. The leading electrodes 105 are connected electrically through a flexible print circuit (FPC) 115 to terminals of the wiring pattern 116 of the drive IC 107.
The leading electrodes 105 are exposed, and each has a width of tens of microns and a thickness of several or some microns. Therefore, when the recording head 100 is assembled, or when it is mounted on a carriage for moving it, the electrodes 105 are liable to come off the head body 101 and break.
The FPC 115 includes a number of signal conductors, which corresponds to the number of leading electrodes 105. Therefore, the electrical connections between the FPC 115 and the electrodes 105 and between it and the terminals of the wiring pattern 116 are complicated. In order to prevent the ink ejected from the nozzles 110 from sticking to the pattern 116 and the drive IC 107, it is preferable that the printed board 119 be protected with resin or the like. If the board 119 is thus protected, however, the heat generated in the IC 107 cannot radiate well.
Japanese Patent application Laid-Open No. 8-112895 discloses an ink jet head, which includes an actuator plate. The plate has first channels formed in it in parallel for ejecting ink. The plate also has second channels, which extend perpendicularly to the first channels and in parallel to their side walls. Each of the second channels communicates with one of the first channels. Formed on the side walls of each first channel are first electrodes, to which actuator drive voltage can be applied. Formed on the side walls of each second channel are second electrodes (ejection channel lead wires), which are connected electrically to the first electrodes.
U.S. patent application Ser. No. 08/635,655 filed Apr. 22, 1996 discloses an ink jet print head, which includes an actuator plate. A leading pattern for a driver circuit is formed on a board, which is bonded to the actuator plate. The body consisting of the board and the plate has a number of channels formed in it, some of which serve as ink chambers. The partitions between the channels function as actuators. For use as a drive electrode, a conductive film is formed on part of each side surface of each partition by oblique vapor deposition and electroplating in such a manner that it is connected electrically to the leading pattern. The film extends on both the board and the plate. Therefore, voltage can be applied directly from the driver circuit to the drive electrodes.
It is an object of the invention to form integrally in the body of an ink jet print head a plurality of leading electrodes each for connection to the electrode of a piezoelectric actuator, and thereby protect the leading electrodes.
It is another object to simplify electrical connections in an ink jet print head and the mounting of a drive IC on the head body.
It is a further object to make efficient the heat radiation from the drive IC of an ink jet print head.
In accordance with a first aspect of the invention, an ink jet print head is provided, which includes a body having nozzles. The body also has ink passages formed in it to be filled with ink. The passages each communicate with one of the nozzles. The head also includes piezoelectric actuators each for changing the volume of one of the passages to eject ink from the associated nozzle. The actuators have leading electrodes extending through the thickness of the body.
As stated above, the leading electrodes of the actuators extend through the thickness of the head body perpendicularly to the ink passages. This prevents the electrodes from being damaged or broken when the print (recording) head is assembled or mounted on a carriage. One end of each leading electrode is exposed to the outside of the head body. Therefore, a drive circuit for the actuators can be connected directly to the exposed ends of the electrodes. Consequently, the IC chip including the circuit can be mounted directly on the body. This simplifies the structure of the head, and particularly its electrical connections, and accelerates the radiation of heat from the chip through the body.
The print head may further include second leading electrodes embedded in the head body for connecting the drive circuit to an electric system outside the head. The ends of the second electrodes may be exposed to the outside of the body. In this case, one end of each second leading electrode can be connected to the actuator drive circuit, and the other can be connected to wiring for supplying the circuit with data signals, a drive voltage, etc. It is therefore possible to simplify the electrical connections between the head and an external circuit, and between the drive circuit and the external circuit.
In accordance with a second aspect of the invention, an ink jet printer is provided, which comprises a print head and a device for supplying the head with ink. The head includes a body having nozzles. The body also has ink passages formed in it to be filled with ink. The passages each communicate with one of the nozzles. The head also includes piezoelectric actuators each for changing the volume of one of the passages to eject ink from the associated nozzle. The actuators have leading electrodes extending through the thickness of the body.
As stated above, the leading electrodes of the actuators extend through the thickness of the head body. This prevents the electrodes from being damaged or broken when the print (recording) head is assembled or mounted on a carriage. It is possible to make the head compact, thereby making the printer small. It is also possible to reduce the printer trouble or failure due to wiring breakage or the like.
In accordance with a third aspect of the invention, a process is provided for producing a print head for ejecting ink through nozzles by means of piezoelectric actuators. The process comprises the steps of:
laminating green sheets together in which predetermined areas are replaced with materials for forming leading electrodes for the actuators;
sintering the laminated sheets to form a sintered body;
polarizing the sintered body; and
forming ink passages in the sintered body, the passages each communicating with one of the nozzles.
This process includes laminating the green sheets to form the piezoelectric sintered body. Those areas of the sheets, where the leading electrodes are programmed to be formed, are replaced in advance with the materials for forming these electrodes. Therefore, the laminating and sintering of the sheets connect the materials across the thickness of the sheets, forming the electrodes extending across the sheet thickness. The process makes it possible to produce, with high accuracy and ease, a print head having a body through which the leading electrodes of piezoelectric actuators extend.
The process may also comprise the step of mounting on the print head a circuit for driving the head in such a manner that the circuit is connected to those ends of the leading electrodes which are exposed to the outside of the sintered body. Because of the electrode ends exposed in a surface of the sintered (head) body, it is easy to mount directly on the body the IC chip including the circuit for driving the head.
The process may further comprise the step of forming electrodes for driving the piezoelectric actuators on the side walls of the ink passages in such a manner that the driving electrodes are each connected to one of the leading electrodes.
The ink passages may each take the form of a channel. The process may further comprise the step of fitting a cover plate on the sintered body in such a manner that the plate covers the passages. The plate may be another sintered body. The two sintered bodies may be polarized in the opposite directions. The plate may have channels formed in it and each facing one of the channels in the head body (see FIG. 13).